0%

### 题目描述

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (`push`, `peek`, `pop`, and `empty`).

Implement the MyQueue class:

• `void push(int x)` Pushes element x to the back of the queue.
• `int pop()` Removes the element from the front of the queue and returns it.
• `int peek()` Returns the element at the front of the queue.
• `boolean empty()` Returns `true` if the queue is empty, `false` otherwise.

### 例子

#### 例子 1

Input:
`["MyQueue", "push", "push", "peek", "pop", "empty"]`
`[[], [1], [2], [], [], []]`
Output: `[null, null, null, 1, 1, false]`
Explanation:

Can you implement the queue such that each operation is `amortized O(1)` time complexity? In other words, performing `n` operations will take overall `O(n)` time even if one of those operations may take longer.

### Note

You must use only standard operations of a stack, which means only `push to top`, `peek/pop from top`, `size`, and `is empty` operations are valid.
Depending on your language, the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack’s standard operations.

### 解题思路

• 时间复杂度:
• `push: O(n)`
• `pop: O(1)`
• `peek: O(1)`
• `empty: O(1)`
• 空间复杂度: `O(n)`

GitHub 代码同步地址： 232.ImplementQueueUsingStacks.cpp

GitHub: Leetcode-C++-Solution